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At least 325 records · Page 18

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NASA NTRS1971

A survey of Kaufman thruster cathodes.

A survey is presented of various cathodes which have been developed and used in the Kaufman ion thruster. The electron-bombardment type ion source used in the thruster is briefly described. The general design, operating characteristics, and power requirements are shown for each type of cathode from the refractory metals used in 1960 to the plasma discharge hollow cathodes of today. A detailed discussion of the hollow cathode is given describing starting and cyclic operating characteristics as well as more fundamental design parameters. Tests to date show that the plasma hollow cathode is an efficient electron source with demonstrated durability over 10,000 hours and should offer further performance and life improvements.

Weigand, A. J.↗

NASA NTRS1972

Planetary exploration with electrically propelled vehicles.

The characteristics of propulsion systems required for carrying out flight missions within the solar system, as desired by planetary physicists and astronomers, are reviewed. It is shown that an encouraging answer to these requirements is available in the form of electrostatic or ion propulsion systems. The design and performance characteristics of an electrostatic thrustor employing an ion source, accelerating electrode, beam neutralizer, and power source are discussed, together with those of the Kaufmann engine (electrostatic thrustor employing bombardment type ionization). More demanding missions which will become feasible with the advent of nuclear-electric power sources (such as the incore thermionic reactor) may include close orbiters around all the planets, and asteroid and cometary missions.

Stuhlinger, E.↗

NASA NTRS1972

An evaluation of pyrolytic techniques with regard to the Apollo 11, 12 and 14 lunar samples analyses.

The first technique involved pyrolysis at 700 C under an inert atmosphere in a flowing He system at normal pressure. The products were collected at liquid nitrogen temperature and then allowed to pass instantaneously into a combined capillary gas chromatograph-mass spectrometer. The second technique consisted of a vacuum pyrolysis where the sample was first degassed at 150 C and then pyrolized at 500 C and 1000 C consecutively. The products were again collected at liquid nitrogen temperature and then they were directly introduced to the ion source of the mass spectrometer through a modified gas inlet system. The experiments have shown the importance of taking into account the factors that influence pyrolytic degradation and/or the synthesis of products. Pyrolysis of Apollo 14 lunar fines and scrapings from an astronaut's glove gave different products by mass spectroscopy and showed different looking flaky materials upon scanning electron microscopy.

Nagy, B.↗

NASA NTRS1973

Study of neutral composition of lower thermosphere at Fort Churchill.

On Feb. 4 and 6, 1969, and May 11, 1970, Aerobee rockets carrying neutral mass spectrometers were flown at Fort Churchill, Canada during conditions of low geomagnetic activity. As in earlier flights at White Sands, New Mexico, each rocket carried both 'open' and 'closed' ion source instruments. Vertical profiles of N2, O2, O, Ar, and He were measured. Results obtained were essentially the same as those observed at White Sands except that for the winter flights helium appeared to be in diffusive equilibrium.

Nier, A. O.↗

NASA NTRS1974

A field-ionization neutral-particle mass spectrometer

Description of laboratory model of a neutral-particle mass spectrometer that could make localized direct measurements of the neutral densities at 1 AU. Using a magnet that has a circular pole face 2.54 cm in diameter and a gap flux density of 8.0 kG, the following sensitivities were obtained for the various species: 10 to the 10th power counts per second per Torr for H2, 3 times 10 to the eighth power counts per second per Torr for He, and 2 times 10 to the 9th power counts per second per Torr for N2. Overall sensitivity may be increased through the use of electrostatic focusing elements between the ion source and the magnetic analyzer.

Curtis, C. C.↗

NASA NTRS1974

The repulsive 1 Sigma g/+/ He2 potential obtained from total cross sections

An improved apparatus for obtaining short-range molecular potentials is described. The setup is a refined version of that used by Jordan-Amdur and by Leonas. The ion source is provided with a mass analyzing magnet, the capacitance manometer in the scattering cell is calibrated with a McCleod gauge, and the detection unit substitutes a Channeltron multiplier for the thermopile. The measured ground-state He-He potential for radii between 0.49 and 1.56 A is approximately V(r) = 215 x exp(-3.95r) eV, which is 25% higher than the earlier experiments. The result is supported by molecular orbital and statistical model calculations.

Foreman, P. B.↗

NASA NTRS1974

Content of lithium, beryllium, boron, and titanium, and the isotopic composition of lithium, boron, and magnesium in Luna 16 regolith sample

The abundance of the following elements in the L 16-19 No. 118 regolith sample, zone V was determined by isotopic dilution using a mass spectrometer equipped with a scattering ion source: Li -- 9.8, Be -- 1.2, Be -- 2.6, and Ti -- 1.92 percent. For comparison, these same elements were measured in samples of surface material returned by Apollo 11, Apollo 12, and Apollo 14, and in the terrestrial reference standard diabase W-1. The content of Li, Be, and B in the Luna 16 sample is nearly the same as in the Apollo 11 surface material. The surface material returned by Apollo 12 and Apollo 14 contains two to four times more of these elements. However, the abundance ratios of Li, Be, and B are remarkably similar in the surface materials from the four different lunar regions. With respect to basaltic achondrites and especially with respect to chondrites, the lunar basalts are enriched in Li, Be, and B up to 100 times.

Eugster, O.↗

NASA NTRS1975

Practical aspects of plasma processes in thermionic energy converters

Over a decade of cesium vapor thermionic converter research has yielded sufficient understanding of the basic plasma processes to permit application of this understanding to improvement of converter performance. A performance index is defined which relates such converter improvements directly to increases in system performance. A prime practical objective of current research is to reduce or eliminate the arc potential drop presently required to sustain the plasma in the ignited cesium diode. This will substantially increase the energy conversion efficiency, and will permit operation at substantially lower emitter temperatures without requiring lower collector (heat rejection) temperature. Present work is concentrating on evaluating and reducing to practice the several methods employing auxiliary ion sources to eliminate the arc drop which were demonstrated over a decade ago: i.e., various ignited and unignited triode concepts, and the pulse-enhanced diode and triode. These methods are reviewed in light of present understanding and recent experimental data.

Rasor, N. S.↗

NASA NTRS1977

Investigation of hydrogen and helium pumping by sputter ion pumps for Jupiter and outer planets mass spectrometer

The phenomena of ion pumping is reviewed with emphasis on the pumping mechanism for hydrogen and helium. The experimental tests measure the performance of a small, flight proven ion pump which has a nominal four liter/second pumping speed for air. The speed of this pump for hydrogen and helium, and for hydrogen/helium mixes, is presented with particular detail regarding the time dependence. Pump test results are related to anticipated performance of the mass spectrometer by the pumping speeds for the gases to the partial pressure in the ion source. From this analysis, the pump specifications are quantified in terms of mission goals and in terms of observed pumping speeds for the various gases, load levels, and time periods.

Scott, B. W.↗

NASA NTRS1976

Advanced thermionic energy conversion: Joint highlights

A theoretical model was used to study the effects of structured electrodes on converter I-V characteristics and results are given. An auxiliary-ion-source triode operated as a plasmatron was used for studying the enhancement distribution and magnetic effects, and results are reported. Design features of the high current-zero power (ZEPO) converter tests are given.

Source record↗

NASA NTRS1976

The plasmatron: Advanced mode thermionic energy conversion

A theory of the plasmatron was developed. Also, a wide range of measurements were obtained with two versatile, research devices. To gain insight into plasmatron performance, the experimental results are compared with calculations based on the theoretical model of plasmatron operation. Results are presented which show that the plasma arc drop of the conventional arc (ignited) mode converter can be suppressed by use of an auxiliary ion source. The improved performance, however, is presently limited to low current densities because of voltage losses due to plasma resistance. This resistance loss could be suppressed by an increase in the plasma electron temperature or a decrease in spacing. Plasmatron performance characteristics for both argon and cesium are reported. The argon plasmatron has superior performance. Results are also presented for magnetic cutoff effects and for current distributing effects. These are shown to be important factors for the design of practical devices.

Hansen, L. K.↗

NASA NTRS1976

The plasmatron as an advanced performance thermionic converter

A study concerned with the improvement of thermionic converter performance has shown that the plasma arc drop of the conventional arc (ignited) mode converter can be suppressed by use of an auxiliary ion source as in a plasmatron converter. However, this improved performance is now limited to low current densities and narrow interelectrode spacings because of voltage losses due to plasma resistance. An examination of plasmatron performance characteristics for both argon and cesium plasma has shown that the argon plasmatron is superior.

Hansen, L. K.↗

NASA NTRS1977

Optical properties of ion beam textured metals

Copper, silicon, aluminum, titanium and 316 stainless steel were textured by 1000 eV xenon ions from an 8-cm diameter electron bombardment ion source. Copper, silicon, and aluminum developed a cone structure with an average peak-to-peak distance ranging from 1 micron for silicon to 6 microns for aluminum. Titanium and 316 stainless steel developed a serpentine ridge structure. The average peak-to-peak distance for both of these materials was 0.5 micron. Total reflectance for air mass 0 and 2, solar absorptance, and total emittance, normalized for a 425 K black body were calculated from the reflectance measurements. All materials had solar absorptances between 0.93 (stainless steel) and 0.97 (silicon and aluminum). Total emittance values of 0.75, 0.80, and 0.85 for Si, Al, and Cu, respectively, resulted in a solar absorptance/total emittance ratio of approximately 1.2. Titanium and 316 stainless steel had values of 2.6 and 2.9, respectively, for this ratio.

Hudson, W. R.↗

NASA NTRS1978

A feasibility study of ion implantation techniques for mass spectrometer calibration

An experimental study was undertaken to examine the feasibility of using ion-implanted filaments doped with either an alkali metal or noble gas for in situ recalibration of onboard mass spectrometers during extended space missions. Implants of rubidium and krypton in rhenium ribbon filaments were subsequently tested in a bakeable 60 deg sector mass spectrometer operating in the static mode. Surface ionization and electron impact ion sources were both used, each yielding satisfactory results. The metallic implant with subsequent ionization provided a means of mass scale calibration and determination of system operating parameters, whereas the noble gas thermally desorbed into the system was more suited for partial pressure and sensitivity determinations.

Koslin, M. E.↗

NASA NTRS1978

A technique for mass spectrometer measurements of atomic and molecular oxygen in the lower thermosphere

A neutral mass spectrometer with a quasi-open ion source was flown on each of the Atmosphere Explorer (AE) C, D, and E satellites. The three instruments provided an opportunity to study the effects of different source insert materials on the source surface chemistry. It was found that, after a period of conditioning in space, the recombination coefficient of atomic oxygen on gold appears to be substantially lower than it is on Nichrome V. The lower recombination coefficient on gold allows the spectrometer to directly measure a significant fraction of the incident atomic oxygen, making it possible to distinguish between ambient O and O2. Equations are developed to calculate the atomic and molecular oxygen densities. Preliminary measurements of molecular oxygen densities obtained by this technique agree well with measurements taken in the fly-through mode of operation.

Kayser, D. C.↗

NASA NTRS1979

Diffusion and phase change characterization by mass spectrometry

The high temperature diffusion of trace elements in metals and alloys was investigated. Measurements were made by high sensitivity mass spectrometry in which individual atoms were detected, and quantitative data was obtained for zircaloy-2, 304 stainless steel, and tantalum. Additionally, a mass spectrometer was also an analytical tool for determining an allotropic phase change for stainless steel at 955 C, and a phase transition region between 772 C and 1072 C existing for zircaloy-2. Diffusion rates were measured in thin (0.001" (0.0025 cm) and 0.0005" (0.0013 cm)) ribbons which were designed as high temperature thermal ion sources, with the alkali metals as naturally occurring impurities. In the temperature and pressure regime where diffusion measurements were made, the solute atoms evaporated from the ribbon filaments when the impurities diffused to the surface, with a fraction of these impurity atoms ionized according to the Langmuir-Saha relation. The techniques developed can be applied to many other alloys important to space vehicles and supersonic transports; and, with appropriate modifications, to the diffusion of impurities in composites.

Koslin, M. E.↗

NASA NTRS1979

The Addition of EI/CI Capability to the Mattauch-herzog Spectrograph with EOID

A modification was made to the Mattauch-Herzog Spectrograph with an electro-optical ion detector (EOID) previously designed and constructed, so that it would be capable of operating not only in the electron-impact (EI) mode of ionization, but also in the chemical ionization (CI) mode. This modification necessitated an effort in three specific design areas: (1) sample inlet; (2) ion source and analyzer regions; and (3) the pumping system. In addition, an appropriate electronics package had to be designed to control and operate the combined EI/CI source.

Fergusson, G. J.↗

NASA NTRS1979

Pioneer Venus large probe neutral mass spectrometer

The Pioneer Venus large probe neutral mass spectrometer (LNMS) uses a single focusing magnetic sector field mass analyzer with mass range of 1-208 amu, resolution sufficient to separate the mercury isotopes, and sensitivity sufficient to detect minor constituents in the 1 ppm range relative to the CO2 in the Venus atmosphere. A combination of ion and chemical pumping is used to maintain a vacuum in the mass analyzer and to remove the atmosphere gases which enter the ion source chamber through a special leak. A microprocessor controls the operation of the instrument through a highly efficient peak stepping and data compression program, permitting acquisition of a complete mass spectrum roughly once each minute.

Hoffman, J. H.↗